It is well known to use a video camera with a computer frame grabber. A typical system employs a video motion camera (such as the CCD 4000 RGB Flash-Sync Camera manufactured by Eastman Kodak Co., Rochester, N.Y.) and a frame grabber board (such as a TARGA.TM. frame store board manufactured by True Vision, Inc., Indianapolis, Ind.) attached to the PC bus of a personal computer. The camera provides the timing to interface with the video frame store board by activating the frame acquire line of the frame store board whenever an external voltage input to the camera is dropped low (e.g., by dropping the "Camera Acquire In" line to the CCD 4000 camera). It is customary to design software to activate the camera's frame acquire line from the computer. To capture an image into the computer in such a customary application, the operator frames the subject while observing the live camera output on a video monitor, and then interacts with the computer keyboard at the proper moment.
Another approach to computer image acquisition is described in U.S. Ser. No. 805,220, entitled "Hand-Manipulated Electronic Camera Tethered to a Personal Computer," which was filed Dec. 11, 1991 in the names of K. A. Parulski, R. H. Hamel, and J. J. Acello, and assigned to the assignee of the present application. In this system an electronic camera is coupled to a personal computer through a computer interface. In particular, a digital interface standard may be used, and images from the camera are input to the computer through a Small Computer System Interface (SCSI). The camera is preferably linked, or tethered, to the computer with a cable, thus allowing a certain amount of mobility for the camera independent of the computer.
Both of these known interfaces have drawbacks. The NTSC signal is an analog signal subject to noise, and additionally requires a special frame grabber card in the computer to decode and digitize the signal. The SCSI signal has a relatively low data rate and a complicated protocol, requiring an expensive SCSI interface integrated circuit in the camera. Notwithstanding such drawbacks, the system described in Ser. No. 805,220 provides a low cost electronic still camera which attaches to a personal computer that provides image processing, storage, and display. By relying on the computer to perform these tasks, the camera cost can be greatly reduced.
It is known to provide detachable integrated circuit memory in the size and form of a thin card, much like a credit card, that is connectable to a memory card reader which interfaces to a host data processing system via a standard interface, such as the SCSI interface. A typical general-purpose host system, such as a desktop computer, incorporates a processor for utilizing data recorded on the memory card in a variety of applications; a typical specialized host system, e.g., an image capture processing system, provides large volumes of digital data for rapid recording on the card. Newer, smaller, battery-operated personal computers (such as notebook or penpad personal computers) utilize a memory card controller (such as the MB86301 Memory Card Controller, by Fujitsu Microelectronics, Inc.) that is compatible with the Personal Computer Memory Card International Association (PCMCIA) standard. Such a controller is capable of interfacing a variety of memory cards, with densities up to 64 Mbytes, to a wide range of microprocessors via 8- or 16-bit data paths. A typical application is shown in FIG. 1, where a small, battery-operated computer 10 includes a card receptacle 12 for accepting a memory card 14. These computers are often ergonomically designed so that the display screen 11 folds over the keyboard 13, making a very compact package. In such a computer the memory card 14 takes the place of a floppy disk drive. Such small computers often have an RS-232 input port 15, but seldom have either a SCSI port or a dedicated video input port. Images can be input via the RS-232 port 15, but this is a very slow process.
A memory card may also be used as the removable storage medium for recording images taken by an electronic still camera. An example of such a system is shown in U.S. Pat. No. 5,016,107, wherein an image sensor generates analog image information that is converted into digital signals, transformed, and encoded into a compressed stream of digital signals that are downloaded to a removable memory card. The memory card disclosed therein includes a commercially-available high speed static random access memory (SRAM). In another configuration of interest, which is shown in U.S. Pat. No. 4,937,676, a compact, handheld portable electronic imaging system includes both an electronic imaging camera and a hard copy printer (and display) that are separately housed with respect to each other yet readily interconnectable for use either in combination or apart. The camera and printer interconnect by means of an elongated tongue member on the printer housing that slides into a recessed groove in the camera housing. Electrical connectors in the tongue-groove interface convey image signals between the camera and the printer. In addition to the tongue-groove interface between the camera and the printer, slots are provided on the respective units to accept memory cards for separate storage and retrieval of the image signals.
In all of these systems, there is need for a low cost means of digitally interfacing a small camera peripheral to a portable computer at a rate higher than that provided by a SCSI interface or an RS-232 input, and without the attendant difficulties of an analog frame grabbing process.